Since multimedia applications are becoming more and more popular, the video compression techniques are also becoming increasingly important. The main principle of these compression techniques is to eliminate redundancy among successive frames to reduce the storage requirement and the amount of transmission data. Intra prediction and inter prediction are two new coding techniques developed by H.264/AVC compression standard. The intra prediction technique utilizes the spatial correlation among neighboring blocks within one frame, while the inter prediction technique utilizes the temporal correlation among consecutive frames.
Referring to intra prediction, the H.264/AVC compression standard defines both of intra 4×4 and intra 16×16 luma prediction modes. There are nine optional prediction modes for each 4×4 luma block and four optional prediction modes for each 16×16 luma block. Referring to FIG. 1A, the region indicated by the bold line is a 4×4 block to be predicted, which is consisted of pixels a-p, neighboring with coded pixels A-Z. FIGS. 1B and 1C depict the directions and implements of the nine 4×4 prediction modes respectively, which use the pixel values of the border pixels A-M to replace the values of the pixels a-p. Modes 0-8 contain one vertical prediction mode, one horizontal prediction mode, one DC prediction mode, and six diagonal prediction modes. In the DC prediction mode (mode 2), each of the pixels a-p is replaced by an average of pixel values of the border pixels A-M. Further, for the remaining prediction modes, the manners for replacing the pixels are illustrated by the arrows shown in FIG. 1C. More information regarding the nine prediction modes can be found in Draft ITU-T Recommendation and Final Draft International Standard of Joint Video Specification (ITU-T Rec. H.264|ISO/IEC 14496-10 ACV), p. 100˜102. After performing the nine prediction modes, error between the predicted pixel value and the original pixel value of the 4×4 block is calculated for each prediction mode. Then, the mode with minimum error will be adopted for coding.
FIG. 2 is a diagram illustrating four 16×16 prediction modes, wherein H and V represent coded pixels. Similar to the 4×4 block, the mode with minimum error will be adopted. Typically, 16×16 prediction mode is preferable to the flatter region (such as background) to reduce the bit number needed for coding.
After being compressed, the video data are transformed into video bitstreams which are suitable for transmission and store. However, transmission of highly compressed video bitstreams can suffer from packet erasures (especially in regard to wireless video transmission). In order to avoid the degradation in quality of the received video frames caused by video packet erasures, three mechanisms are commonly used to guard against possible packet losses: automatic retransmission request (ARQ), forward error correction (FEC), and error concealment. Comparing with the ARQ and FEC techniques, the error concealment technique does not require additional bandwidth and is especially useful in multicast and broadcast situations. The error concealment technique executed at the video decoder can be classified into two types: spatial error concealment and temporal error concealment. The spatial error concealment utilizes spatial redundancy information in a frame to recover the damaged video sequences, while the temporal error concealment exploits the highly correlation among consecutive frames of the coded sequence to reconstruct the damaged video sequences.
Since the spatial error concealment approach utilizes the spatial redundancy information in a frame without reference to other frames, it is much preferable to the temporal error concealment approach in the presence of scene changes, the appearance and disappearance of objects, irregular motion of objects, especially as errors happen in the initial frame. Other disclosures relating to spatial error concealment approach include “Spatial error concealment of corrupted image data using frequency selective extrapolation” by Meisinger et al., Proc. Int. Conf. Acoust., Speech, Signal Process. (ICASSP), 2004, pp. 209-212; “Error concealment in encoded video streams” by Salama et al., Signal Recovery Techniques for Image and Video Compression and Transmission, 1998, ch. 7; “The error concealment feature in the H.26L test model”, by Wang et al., Proc. Int. Conf. Image Processing (ICIP), Rochester, N.Y., USA, September 2002, vol. 2, pp. 729-732; “Maximally smooth image recovery in transform coding” by Wang et al., IEEE Trans. Commun., vol. 41, pp. 1544-1551, October 1993; “Coding and cell loss recovery for DCT-based packet video” by Zhu et al., IEEE Trans. Circuits Syst. Video Technol., vol. 3, pp. 248-258, June 1993; “Transform coded image reconstruction exploiting interblock correlation” by Hemami, IEEE Trans. Image Processing, vol. 4, pp. 1023-1027, July 1995; “DCT coefficients recovery-based error concealment technique and its application to MPEG-2 Bit stream error” by Park et al., IEEE Trans. Circuits and Systems for Video Technology, vol. 7, pp. 845-854, December 1997; “Fast DCT based spatial domain interpolation of blocks in images” by Alkachouh et al., IEEE Trans. Image Process., vol. 9, no. 4, pp. 29-732, April 2000; “Content-adaptive spatial error concealment for video communication” by Rongfu et al., IEEE Trans. Consum. Electron., vol. 50, no. 1, pp. 335-341, January 2004; “Enhanced error concealment with mode selection” by Agrafiotis et al., IEEE Trans. Circuits Syst. Video Technology, vol. 16, no. 8, pp. 960-973, August 2006; and “Optimization of Spatial Error Concealment for H.264 Featuring Low Complexity” by Huang et al., Proc. Int. Conf. MultiMedia Modeling (MMM), January 2008, LNCS 4903, pp. 391-401, the entire contents of which being incorporated herein by reference.
Many researches for improving the spatial error concealment approach have been proposed, but the problem of heavy computation load still exists. Therefore, it is desirable to provide a method capable of both reducing computation complexity of the spatial error concealment and maintaining the display quality.